Coupling device and folding electronic apparatus using the same

ABSTRACT

A hinge mechanism includes flanges  23 A,  23 B, and a swivel mechanism includes swiveling shaft  25.  Spring  26  energizes the swiveling mechanism. Resilient repulsion of spring  26  torqued energizes the swiveling mechanism to swivel toward either end of a swivelable range.

FIELD OF THE INVENTION

[0001] The present invention relates to a coupling device which connects two electronic apparatuses having functions relative to each other and allows the two apparatuses to be folded as well as to be swiveled, and it also relates to a folding electronic apparatus using the same coupling device.

BACKGROUND OF THE INVENTION

[0002]FIG. 17 is a perspective outline drawing of a folding hand-held electronic apparatus disclosed in Japanese Patent Application Non-Examined Publication No. H11-30226. A conventional coupling device shown in FIG. 17 comprises hinge mechanism 5 and swivel mechanism 6.

[0003] Hinge mechanism 5 connects first flat electronic apparatus 2 having display 1 to second flat electronic apparatus 4 having operating board 3 such that apparatus 2 and apparatus 4 can be folded.

[0004] Swivel mechanism 6 is disposed between first apparatus 2 and hinge mechanism 5 and allows a user to swivel first apparatus 2 arbitrarily. As shown in FIG. 18 and FIG. 19, the hand-held electronic apparatus can be folded in two ways, i.e., (1) display 1 of first apparatus 2 shows inside and faces closely to operating board 3 of apparatus 4, and (2) contrary to case (1), display 1 shows outside.

[0005] Swivel mechanism 6 includes cylinder 7 and cylinder 8 fitted to each other, and this fitting allows both of cylinders 7 and 8 to swivel, as shown in a sectional view of FIG. 20. First apparatus 2 is mounted to cylinder 7, and cylinder 8 is mounted to hinge mechanism 5. Spring 13 urges cylinder 7 against cylinder 8 in order to supply a predetermined frictional resistance to the swiveling of first apparatus 2.

[0006]FIG. 21A and FIG. 21B illustrate each end face, opposite to each other, of cylinder 7 and cylinder 8 respectively. Protrusion 9 and guide groove 10 regulate a swivelable range of first apparatus 2 from its front side to reverse side, i.e., turned over. Protrusion 12 and recess 14 hold first apparatus 2 at either end of the swivelable range by clicking apparatus 2 into place with pressure of spring 13.

[0007] However, in the hand-held electronic apparatus using the conventional coupling device discussed above, when first apparatus 2 and second apparatus 4 are in an open position as shown in FIG. 17, first apparatus 2 can be stopped at an intermediate place within the swivelable range. If a user carelessly folds the hand-held electronic apparatus when first apparatus 2 is held vertical to second apparatus 4, a corner of first apparatus 2 may damage second apparatus 4.

SUMMARY OF THE INVENTION

[0008] The present invention aims to provide a coupling device, which addresses the problem discussed above, of a folding electronic apparatus. The coupling device of the present invention connects a first electronic apparatus to a second electronic apparatus. Both of the apparatuses are included in a hand-held electronic apparatus.

[0009] The coupling device comprises the following elements:

[0010] (a) a hinge mechanism;

[0011] (b) a swivel mechanism; and

[0012] (c) a spring for energizing the swivel mechanism.

[0013] The spring is mounted to the swivel mechanism such that the spring is strongly torqued when the first apparatus is at the middle in a swivelable range, and the torque decreases gradually as the first apparatus approaches either end of the swivelable range. Resilient repulsion of the torqued spring energizes the swivel mechanism to swivel the first apparatus toward either end of the swivelable range. As a result, the first apparatus stops and stays still at an end of the swivelable range. When the first apparatus stays at the end of the range, the first apparatus is held in parallel with the second apparatus, therefore, the second apparatus is not damaged when the handheld electronic apparatus is folded.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a perspective outline drawing of a coupling device in accordance with a first exemplary embodiment of the present invention.

[0015]FIG. 2 shows a perspective exploded view of the coupling device in accordance with the first exemplary embodiment.

[0016]FIG. 3 is a perspective outline drawing of a folding cellular phone.

[0017]FIG. 4 shows a perspective exploded view of the folding cellular phone shown in FIG. 3.

[0018]FIG. 5 is a perspective outline drawing of a cellular phone folded.

[0019]FIG. 6 is a perspective outline drawing of a cellular phone of which first electronic apparatus swivels a right angle.

[0020]FIG. 7 is a perspective outline drawing of a cellular phone of which first electronic apparatus is turned reversely.

[0021]FIG. 8A-FIG. 8C illustrate how a swivel mechanism works in accordance with the first exemplary embodiment.

[0022]FIG. 9A-FIG. 9C illustrate how a swivel mechanism works in accordance with the second exemplary embodiment.

[0023]FIG. 10 is a perspective outline drawing of a cellular phone of which first electronic apparatus swivels aslant with respect to a second apparatus.

[0024]FIG. 11 is a perspective outline drawing of a coupling device in accordance with a third exemplary embodiment of the present invention.

[0025]FIG. 12 shows a perspective exploded view of the coupling device shown in FIG. 11.

[0026]FIG. 13A-FIG. 13C illustrate how a swivel mechanism works in accordance with the third exemplary embodiment.

[0027]FIG. 14A-FIG. 14C illustrate how a swivel mechanism works in accordance with a fourth exemplary embodiment.

[0028]FIG. 15 is a perspective outline drawing of a coupling device in accordance with a fifth exemplary embodiment of the present invention.

[0029]FIG. 16 shows a perspective exploded view of the coupling device shown in FIG. 15.

[0030]FIG. 17 is a perspective outline drawing of a folding cellular phone using a conventional coupling device.

[0031]FIG. 18 is a perspective outline drawing of a conventional cellular phone folded.

[0032]FIG. 19 is a perspective outline drawing of a conventional cellular phone of which first electronic apparatus is doubled back reversely to what is shown in FIG. 18.

[0033]FIG. 20 shows a sectional view of a conventional swiveling mechanism.

[0034]FIG. 21A and FIG. 21B illustrate each end face of cylindrical members of the conventional swiveling mechanism.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT

[0035] First Exemplary Embodiment

[0036]FIG. 1 is a perspective outline drawing of a coupling device in accordance with the first exemplary embodiment of the present invention, and FIG. 2 shows a perspective exploded view of the same coupling device. Main frame 22 of coupling device 21 includes flange 23A, flange 23B on its respective ends and cylinder 24 at a center of main frame 22. Flanges 23A, 23B have a square hole respectively for receiving second electronic apparatus 31 (hereinafter called “second apparatus”) described later. Cylinder 24 has a through hole 24A running vertically to an axis line extending from a center of square hole 23C to a center of square hole 23D.

[0037] Swiveling shaft 25 is fit in hole 24A in a swivelable way. Flange 25A disposed at a first end of shaft 25 has protrusion 25B on its rim. Two stoppers 24B, 24C (shown in FIG. 8A-FIG. 8C) are provided to circular recess 24E. Protrusion 25B, stoppers 24B, 24C regulate a swivelable range of shaft 25A within 180°.

[0038] Small hole 25C is provided at a center of protrusion 25B, and small hole 24D is provided to main frame 22 at outside a middle point between stoppers 24B and 24C.

[0039] Both ends 26D and 26C of torsion coil spring 26, torqued and made of resilient metallic wire such as piano-wire, are loosely fit in small holes 24D, 25C. Resilient repulsion of torqued spring 26 energizes shaft 25 so that swivels protrusion 25B can hit one of stoppers 24B or 24C.

[0040] A second end 25D of shaft 25 shapes in a non-circular form, and mounting bracket 27 made of metal plate is fixed to end 25D for coupling first electronic apparatus 29 (hereinafter called “first apparatus”) described later.

[0041]FIG. 3 is a perspective outline drawing of a folding cellular phone using coupling device 21 in accordance with the first embodiment, and FIG. 4 shows a perspective exploded view illustrating how this folding cellular phone is assembled. The assembling method comprises the steps of:

[0042] (1) Couple board 29A of first apparatus 29 together with case 29B to mounting bracket 27 with screws 33A and 33B. Board 29A has display 28.

[0043] (2) Overlay cover plate 29C on board 29A, thereby completing first electronic apparatus 29. At the same time, first apparatus 29 is connected to coupling device 21 in a swivelable way.

[0044] (3) Sandwich main frame 22 with holders 34A, 34B provided at an end of case 31B of second apparatus 31, then align square holes 23C, 23D and round holes 34C, 34D, and press-fit pivot pin 35-35. Round root-section 35A of pivot pin 35 loosely fits in round holes 34C, 34D, and a divided square section at tip of pivot pin 35 is press-fitted and fixed in square holes 23C, 23D.

[0045] (4) Connect flexible wired board 36, which is led out from board 29A of first apparatus 29, to board 31A of second apparatus 31.

[0046] (5) Accommodate board 31A into case 31B, and overlay key-board 31C to be used for keying and cover board 31D on board 31A, thereby completing second apparatus 31. At the same time, second apparatus 31 is connected to coupling device 21 in a rotatable way.

[0047] (6) Cover coupling device 21 with covers 32A, 32B, thereby completing the folding cellular phone as shown in FIG. 3.

[0048] As discussed above, coupling device 21 includes a hinge mechanism formed of main frame 22, pivot pin 35 and others, and a swivel mechanism formed of main frame 22, shaft 25 and others. The hinge mechanism connects first apparatus 29 to second apparatus 31 in a foldable way. FIG. 5 shows a cellular phone folded. The swivel mechanism as shown in FIG. 6 holds first apparatus 29 in a swivelable way. FIG. 7 shows a cellular phone of which first apparatus 29 is folded with its face turned up.

[0049] An operation of the swivel mechanism in accordance with the first embodiment is demonstrated with reference to FIG. 8A-FIG. 8C. FIG. 8A shows the swivel mechanism in a normal status (shown in FIG. 3) with its display 28 facing in front. Resilient repulsion of spring 26, of which both ends are inserted into small holes 24D, 25C respectively, energizes the swivel mechanism along the arrow mark such that protrusion 25B is urged to stopper 24B. Then first apparatus 29 (not shown) connected to mounting bracket 27 stops and stays still.

[0050]FIG. 8B shows a status of the swivel mechanism when first apparatus 29 is approx. at the center of the swivelable range and vertical to second apparatus 31. In other words, first apparatus faces laterally second apparatus 31 as shown in FIG. 6. The centers of small holes 24D, 25C and shaft 25E are aligned, which means that first apparatus 29 is at a neutral position of the resilient repulsion of spring 26. Spring 26 can receive the strongest torque at the neutral position. From the status shown in FIG. 8A, a user starts swiveling first apparatus 29 clockwise, then the resilient repulsion of spring 26 resists the swiveling on the way to the neutral position but assists the swiveling after first apparatus 29 passes the neutral position. If the user takes a hand off first apparatus 29 before it arrives at the neutral position, apparatus 29 is energized to return to stopper 24B. If the user takes a hand off apparatus 29 after it passes the neutral position, apparatus 29 is energized to move to stopper 24C. In either case, first apparatus 29 swivels to either one of the ends, and stops and stays still at the end. Since the neutral position is unstable, first apparatus 29 hardly stops there.

[0051]FIG. 8C shows a status of the swivel mechanism when display 28 is faced up, i.e., the cellular phone is doubled back and display 28 shows in front. The resilient repulsion of spring 26 energizes the swivel mechanism along the arrow mark such that protrusion 25B is urged to stopper 24C. First apparatus 29 connected to mounting bracket 27 stops and stays still. In this status, when the user folds the cellular phone, display 28 shows in front as shown in FIG. 7.

[0052] Second Exemplary Embodiment

[0053] A coupling device in accordance with the second embodiment is demonstrated with reference to FIG. 9A-FIG. 9C. Elements similar to those in the first embodiment have the same reference marks and the descriptions thereof are omitted here. A construction of coupling device 37 of the second embodiment is similar to that of coupling device 29 of the first embodiment. Only a difference is that small hole 38C, to which end 26D of spring 26 is inserted, is provided to a place at a different angle from small hole 24D of the first embodiment.

[0054] As shown in FIG. 9A-FIG. 9C, small hole 38C is provided on the left side from a middle point between stoppers 24B, 24C. This structure allows the centers of small holes 38C, 25C and center 25E of shaft 25 to be aligned. A neutral position of resilient repulsion of spring 26 locates on the left side from the middle point between stoppers 24B, 24C. Therefore, when first apparatus 29 is at the neutral position, an angle formed by first and second apparatuses 29, 31 can deviate from a right angle. As a result, this structure can reduce damages of the cellular phone when it is folded. Spring 26 receives the strongest torque at the neutral position of the resilient repulsion.

[0055]FIG. 9A shows a normal status of the swivel mechanism with its display 28 facing in front, as shown in FIG. 3. Ends 26D, 26C of spring 26 are inserted in small holes 38C, 25C respectively, and the resilient repulsion of this spring 26 energizes the swivel mechanism along the arrow mark such that protrusion 25B is urged to stopper 24B. First apparatus 29 (not shown) connected to mounting bracket 27 stops and stays still.

[0056]FIG. 9B shows a status of the swivel mechanism when first apparatus 29 is at the neutral position of the resilient repulsion of spring 26. The neutral position is on the left side from a middle point between stoppers 24B and 24C. First apparatus 29 thus does not face second apparatus 31 at a right angle, but it faces second apparatus 31 in a laterally slanted (aslant) manner as shown in FIG. 10. From the status shown in FIG. 9A, a user starts swiveling first apparatus 29 clockwise, then the resilient repulsion of spring 26 resists the swiveling on the way to the neutral position. However, the repulsion assists the swiveling after first apparatus 29 passes the neutral position, as shown by arrow marks in FIG. 9B.

[0057]FIG. 9C shows a status of the swivel mechanism when display 28 is faced up, i.e., the cellular phone is doubled back and display 28 shows in front. The resilient repulsion of spring 26 energizes the swivel mechanism along the arrow mark such that protrusion 25B is urged to stopper 24C. First apparatus 29 connected to mounting bracket 27 stops and stays still. In this status, when the user folds the cellular phone, display 28 shows in front as shown in FIG. 7.

[0058] Because the neutral position is unstable, first apparatus 29 hardly stops at the neutral position shown in FIG. 9B. However, it stops there sometime anyway. Even if first apparatus 29 stops at the neutral position, first apparatus 29 does not face second apparatus 31 at a right angle, but it escapes from a place where the right angle is formed with second apparatus 31. Therefore, if first apparatus 29 is overlaid onto second apparatus 31 by folding, and a corner of apparatus 29 hits operating board 30 of apparatus 31, the corner slips on the operating board, and apparatus 29 deviates from the neutral position. Then spring 26 energizes first apparatus 29 to swivel to either one of the stoppers nearer to the slipped position. Therefore, first apparatus 29 or second apparatus 31 is scarcely damaged.

[0059] Third Exemplary Embodiment

[0060] A coupling device in accordance with the third embodiment is demonstrated hereinafter. Elements similar to those in the previous embodiments have the same reference marks and the descriptions thereof are omitted here. FIG. 11 is a perspective outline drawing of the coupling device, and FIG. 12 shows a perspective exploded view of the same coupling device. Main frame 40 of coupling device 39 includes flanges 40A, 40B at respective ends and cylinder 41 at the center. Flanges 40A, 40B have square holes 40C, 40D respectively. Cylinder 41 has a through-hole 41A running vertically to an axis line extending between each center of square holes 40C, 40D. Swiveling shaft 42 fits to hole 41A in a swivelable way. Flange 42A at a first end of shaft 42 has protrusion 42B on its rim. Two stoppers 41B, 41C are provided to circular recess 41D. Protrusion 42B and stoppers 41B, 41C regulate a swivelable range within 180°. Shaft 42 has protrusion 42C on an end face of flange 42A at a place nearer to protrusion 42B. Protrusion 42C has side face 42E which bows outward. If there is no problem in strength, protrusion 42C may be a protrusion of which sectional view shapes in a circle or a semi-circle. Mounting bracket 27 is fixed to a second end, which is noncircular section 42D, of shaft 42.

[0061] A pair of slits 40E (not shown), 40F are disposed inside flanges 40A, 40B respectively. Holding section 43A of spring 43 made from elastic thin metal plate is press-fitted downward into slits 40E, 40F, and held in the slits. Claws 43B prevent holding section 43A from coming off. Linear section 43E of spring 43 urges elastically protrusion 42C of shaft 42 with a given pressure.

[0062] A method of assembling a folding cellular phone, which uses coupling device 39 discussed above, is the same as demonstrated in the first embodiment. The description of the assembling method is thus omitted here.

[0063] An operation of a swivel mechanism in accordance with the third embodiment is demonstrated with reference to FIG. 13A-FIG. 13C. FIG. 13A illustrates a normal status (as shown in FIG. 3) of the swivel mechanism, i.e., display 28 faces in front. Linear section 43E of spring 43 urges elastically a side face of protrusion 42C. Resilient repulsion of spring 43 energizes the swivel mechanism along the arrow mark such that protrusion 42B is urged to stopper 41B. First apparatus 29 (not shown) connected to mounting bracket 27 stops and stays still.

[0064]FIG. 13B shows a status of the swivel mechanism when first apparatus 29 is approx. at the center of the swivelable range and vertical to second apparatus 31. In other words, first apparatus faces laterally second apparatus 31 as shown in FIG. 6. Linear section 43E of spring 43 comes in contact with a top of side face 42E, bowing outward, of protrusion 42C. This means that first apparatus 29 is at a neutral position of the resilient repulsion of spring 43. Spring 43 can receive the strongest torque at the neutral position. From the status shown in FIG. 13A, a user starts swiveling first apparatus 29 clockwise, then the resilient repulsion of spring 43 resists the swiveling on the way to the neutral position but assists the swiveling after first apparatus 29 passes the neutral position. If the user takes a hand off first apparatus 29 before it arrives at the neutral position, apparatus 29 is energized to return to stopper 41B. If the user takes a hand off apparatus 29 after it passes the neutral position, apparatus 29 is energized to move to stopper 41C. In either case, first apparatus 29 swivels to either one of the ends, and stops and stays still at the end. Since the neutral position is unstable, first apparatus 29 hardly stops there.

[0065]FIG. 13C shows a status of the swivel mechanism when display 28 is faced up, i.e., the cellular phone is doubled back and display 28 shows in front. The resilient repulsion of spring 43 energizes the swivel mechanism along the arrow mark such that protrusion 42B is urged to stopper 41C. First apparatus 29 connected to mounting bracket 27 stops and stays still. In this status, when the user folds the cellular phone, display 28 shows in front as shown in FIG. 7.

[0066] Fourth Exemplary Embodiment

[0067] A coupling device in accordance with the fourth embodiment is described with reference to FIG. 14A-FIG. 14C. Elements similar to those in the previous embodiments have the same reference marks and the descriptions thereof are omitted here. A structure of coupling device 44 in accordance with the fourth embodiment is similar to coupling device 39 used in the third embodiment. However, locations of stoppers 41B, 41C and an angle formed by protrusions 42B, 42C are different from those in the third embodiment. Protrusion 42B deviates from protrusion 42C by a given angle.

[0068] This structure allows first apparatus 29, being at a neutral position of resilient repulsion of spring 43, to escape from a right angle with respect to second apparatus 31. Thus damages, incurred when a cellular phone is folded, can be reduced. Spring 43 receives the strongest torque at the neutral position of the resilient repulsion.

[0069]FIG. 14A illustrates a normal status (as shown in FIG. 3) of the swivel mechanism, i.e., display 28 faces in front. Linear section 43E of spring 43 urges elastically a side face of protrusion 42C. Resilient repulsion of spring 43 energizes the swivel mechanism along the arrow mark such that protrusion 42B is urged to stopper 41B. First apparatus 29 (not shown) connected to mounting bracket 27 stops and stays still.

[0070]FIG. 14B shows a status of the swivel mechanism when first apparatus 29 is at the neutral position. Linear section 43E of spring 43 comes in contact with a top of side face 42E, bowing outward, of protrusion 42C. This means that first apparatus 29 is at the neutral position of the resilient repulsion of spring 43. Spring 43 can receive the strongest torque at its neutral position. In this status, first apparatus 29 does not face second apparatus 31 at a right angle, but it faces second apparatus 31 in a laterally slanted (aslant) manner as shown in FIG. 10. From the status shown in FIG. 14A, a user starts swiveling first apparatus 29 clockwise, then the resilient repulsion of spring 43 resists the swiveling on the way to the neutral position but assists the swiveling after first apparatus 29 passes the neutral position. An angle, traveled by first apparatus 29 for swiveling up to the neutral position, is smaller than 90°.

[0071]FIG. 14C shows a status of the swivel mechanism when display 28 is faced up, i.e., the cellular phone is doubled back and display 28 shows in front. The resilient repulsion of spring 43 energizes the swivel mechanism along the arrow mark such that protrusion 42B is urged to stopper 41C. First apparatus 29 connected to mounting bracket 27 stops and stays still. In this status, when the user folds the cellular phone, display 28 shows in front as shown in FIG. 7.

[0072] Since the neutral position is unstable, first apparatus 29 hardly stops at the neutral position shown in FIG. 14B. However, it stops there sometime anyway. Even if first apparatus 29 stops at the neutral position, first apparatus 29 does not face second apparatus 31 at a right angle, but it escapes from a place where the right angle is formed with second apparatus 31. Therefore, if first apparatus 29 is overlaid onto second apparatus 31 by folding, and a corner of apparatus 29 hits operating board 30 of apparatus 31, the corner slips on the operating board, and apparatus 29 deviates from the neutral position. Then spring 26 energizes first apparatus 29 to swivel to either one of the stoppers nearer to the slipped position. Therefore, first apparatus 29 or second apparatus 31 is scarcely damaged.

[0073] In the description above, the neutral position is nearer to stopper 45B than to the middle point of the swivelable range of first apparatus 29. However, the neutral position can be located nearer to another stopper 45C than to the middle point of the swivelable range of first apparatus 29 by reversing a direction of the angle deviation between protrusion 42B, 42C.

[0074] Fifth Exemplary Embodiment

[0075] A coupling device in accordance with the fifth embodiment is demonstrated hereinafter. Elements similar to those in the previous embodiments have the same reference marks and the descriptions thereof are omitted here. FIG. 15 is a perspective outline drawing of the coupling device in accordance with the fifth embodiment, and FIG. 16 shows a perspective exploded view of the same coupling device. Coupling device 47 uses spring 48 formed of metal wire. Spring 48 is made of resilient metal round-wire, such as piano-wire, having undergone a bending process. Tips 48C, 48D of spring 48 are press-fitted and fixed to supporting holes 49A, 49B (not shown) prepared to main frame 49, and linear section 48E of spring 48 is urged to a side face of protrusion 42C.

[0076] Other parts and an operation of coupling device 47 are similar to those described in the third embodiment with reference to FIG. 11-FIG. 13C. The descriptions thereof are thus omitted here. 

What is claimed is:
 1. A coupling device of a folding electronic apparatus, said coupling device for coupling a first electronic apparatus to a second electronic apparatus of the folding electronic apparatus, said device comprising: a hinge mechanism for unfolding the folding electronic apparatus into the first electronic apparatus and the second electronic apparatus, and folding the first electronic apparatus and the second electronic apparatus into the folding electronic apparatus; a swivel mechanism, disposed between said hinge mechanism and the first electronic apparatus, for retaining the first electronic apparatus in a swivelable way within a predetermined swivelable range; and a spring for energizing said swivel mechanism, wherein said spring is mounted to said swivel mechanism such that said spring is torqued greatly when the first electronic apparatus is at a middle point in the swivelable range and the torque lowers as the first electronic apparatus approaches one of ends of the swivelable range, and wherein resilient repulsion of said spring torqued energizes said swivel mechanism such that the first electronic apparatus swivels toward one of the ends of the swivelable range.
 2. The coupling device of claim 1, wherein the swivelable range of the first electronic apparatus is 180°.
 3. The coupling device of claim 1, wherein said swivel mechanism includes a swiveling shaft; wherein said spring for energizing said swivel mechanism is a torsion coil spring, and a first end of the torsion coil spring is retained at a movable point of the swiveling shaft, and a second end is retained at a static point of said coupling device; and wherein both the ends of the torsion coil spring and a center of the swiveling shaft are aligned when the first electronic apparatus swivels by a predetermined angle.
 4. The coupling device of claim 3, wherein both the ends of the torsion coil spring and the center of the swiveling shaft are aligned when the first electronic apparatus is at a middle point between the middle point of the swivelable range and one of both the ends of the swivelable range.
 5. The coupling device of claim 1, wherein said swivel mechanism includes a swiveling shaft which has a protrusion on an end face of the shaft; wherein said spring for energizing said swiveling mechanism includes a linear section at a first end, the linear section elastically urging the protrusion of the shaft, and a second end of said spring is retained stationary by said coupling device; and wherein said spring receives greater torque at the middle point of the swivelable range than at either end of the swivelable range.
 6. The coupling device of claim 5, wherein said spring is made from elastic metal thin plate which has undergone punching and then bending process.
 7. The coupling device of claim 5, wherein said spring is made of resilient metal wire which has undergone bending process.
 8. The coupling device of claim 5, wherein the protrusion provided on the end face of the shaft includes a bowing side face to which the linear section of said spring urges elastically.
 9. The coupling device of claim 5, wherein the protrusion on the end face of the shaft is provided at a predetermined place such that said spring receives strongest torque when the first electronic apparatus is at a middle point between the middle point of the swivelable range and one of both the ends of the swivelable range.
 10. A folding electronic apparatus which connects a first electronic apparatus to a second electronic apparatus with the coupling device as defined in claim
 1. 